1. Field of Invention
This invention is generally related to the building trades and more specifically to building envelope system designs applicable to an exterior window wall system for use in modular construction technology.
2. Description of the Background
In an effort to significantly minimize field erection time, the relatively new construction technology known as Modular Construction Technology (MCT) has continuously gained popularity. In MCT, the entire building is constructed by connecting multiple shop assembled shippable units in the field. Each shippable unit is shop fabricated with mostly completed interior finishes and weather sealed exterior walls. In this type of construction, the horizontal and vertical butt joints between two adjacent units must be sealed and finished in the field with the consideration of construction tolerances between the two adjacent units. Due to this field requirement, the butt joint cover becomes a special aesthetic feature of the wall, making it extremely difficult to maintain a smooth and uninterrupted appearance if a curtain wall or window wall is desired.
In addition, during the process of joining the units together, any exterior wall within a unit must be weather tight against water infiltration. In consideration of all the above difficulties, most buildings constructed by MCT use punched-out windows on the exterior wall. If a curtain wall is desirable on the completed building, providing a weather tight design along the unit perimeters and inserting a curtain wall panel at the unit butt joint locations are extremely difficult, if not impossible, due to the fact that the curtain wall supporting mullions are located outside of the floor slab edge.
If a window wall is desired, extensive design and field execution efforts are required to make the butt joint cover as a special aesthetic feature and to weather seal the butt joints. In addition, window wall systems in today's market are designed for on-floor installation from the interior side, eliminating the need for expensive exterior access equipment in high-rise construction. In MCT, each unit is one floor height sitting on the shop floor and it is desirable to complete interior finishing work such as installing toilets, kitchen countertops, plumbing, electrical, ceiling, drywall, paint, and carpeting, etc. without an enclosed window wall for easy access. Therefore, in MCT, it is desirable to erect the window wall on the unit from the exterior side after the completion of the interior finishing work.
An Airloop window wall system, as described in U.S. Pat. No. 8,001,738, which is hereby incorporated by reference, is particularly desirable for its durable water-tightness performance.